1. Field of the Invention
The present invention relates to an optical switch for use in fiber communication and optical network technology, and particularly to an optical switch having a rotating switching mechanism which is balanced for smooth rotation.
2. Description of Related Art
Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which the optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optic fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals.
In fiber optic systems, various methods have been previously developed for switching optical signals between fiber cables. In these previously developed methods, one important category is mechanical optical switches.
Mechanical optical switches come in two different designs: in one design, the optical components move, and in the other design the fibers move. Factors for assessing the capability of an optical switch include low insertion loss ( less than 1 dB), good isolation performance ( greater than 50 dB) and bandwidth capacity compatible with the fiber network the switch is supporting.
Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a beam of light from one fiber end to another under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses, which expand the beam of light from the fibers, and moving prisms or mirrors, which re-switch the expanded beam as required by the switching process.
The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small portion of the fiber core diameter for two fibers to precisely align to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes the fibers less flexible, increasing the force required to manipulate each fiber into alignment. Thus these moving fiber optical switches share a common problem of requiring high precision parts to obtain precise positioning control and low insertion loss. This results in high costs and complicated manufacture of the switches. Moreover, frequently moving fibers to and fro is apt to damage or even break the fibers.
The moving optical component switches have less stringent movement control tolerance requirements because of the collimating lenses.
For example, as illustrated in FIG. 7, U.S. Pat. No. 5,420,946 discloses an optical switch which comprises an input port, a plurality of output ports and a switching element for switching signals from the input port to one of the output ports. The input port has an input fiber 112 and a collimator 116. The output ports have output fibers 140 and collimators 160. The switching element comprises a base 130, a reflector 124 having a reflecting surface assembled on the base 130, a hole 132 defined in the base 130 for receiving a shaft, and a plate 134 assembled to the base 130 for blocking the light from an optical interrupter 136 to provide reflector 124 position control. The signals from the input fiber 112 are reflected by the reflector 124 to the different output ports according to the rotation of the reflector 124. However, the positions of the input port, the output ports and the reflector must be precisely aligned with one another. Furthermore, the center of inertia of the base 130 and the reflector 124 is difficult to control because of their shapes. Hence, when the base 130 and the reflector 124 are rotated, eccentricity is induced in the shaft driving the base 130, which may lead to problems with the shaft.
As shown in FIGS. 8 and 9, U.S. Pat. No. 6,275,626 discloses an optical switch which comprises an input port 210 having an input fiber 211 and a collimator 212, a plurality of output ports 250 each having an output fiber 251 and a collimator 252, a mirror assembly 228, a driving means 224 and a counterweight 240 attached to the mirror assembly 228. The plurality of output ports 250 is positioned along the circumference of a circle, the center of which is at the position of the input port 210. The mirror assembly 228 is driven to rotate by the driving means 224. Thus, a light beam 218 from the input port 210 is reflected by three surfaces 282, 284, 286 of the mirror assembly 228 to a single output port 250. The mirror assembly 228 achieves balance while rotating about the Y axis by use of the counterweight 240. However, assuring that the center of inertia of the mirror assembly 228 and the counterweight 240 coincides with the axis of rotation is difficult to achieve because of the shape of the mirror assembly 228, which can result in imbalance. Furthermore, the surfaces 282, 284, 286 are formed by coating a highly refractive material on the mirror assembly 228, which is difficult to replace once damaged.
For the above reasons, an improved optical switch which is easy to align and which has a rotating switching mechanism which is balanced for smooth rotation is desired.
An object of the present invention is to provide an optical switch with a rotating switching mechanism which is easy to balance around its axis of rotation.
Another object of the present invention is to provide an optical switch which is easy to align.
An optical switch in accordance with the present invention comprises an input port aligning with an input fiber and having a collimator, a plurality of output ports each aligning with an output fiber and having a collimator, a switching element, and a base.
The switching element has a driving device, a rotary holder attached to the driving device and two reflectors attached to the rotary holder. The rotary holder includes a connecting portion, a supporting arm and two balancing arms to which two counterweights are attached, respectively. The positions of the counterweights on the balancing arms can be adjusted to balance the rotary holder and reflector combination around its axis of rotation.
The base comprises a first wall and a second wall, opposite to one another. The second wall defines a center hole for mounting the collimator of the input port and a plurality of peripheral holes for mounting the collimators of the output ports, respectively. The peripheral holes are evenly positioned around the center hole. The switching element is mounted on the first wall of the base.
The light signals from the input port can be switched to any one of the output ports by rotating the rotary holder and reflector combination driven by the driving device.
The rotary holder and reflector combination is easy to balance about a central axis of the connecting portion by adjusting the positions of the counterweights on the two balancing arms after the two reflectors have been mounted in the rotary holder. Moreover, the reflectors are easily replaced with different mirrors because the positions of the counterweights on the two balancing arms can be adjusted.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.